An ECS card in itself shouldn't be a problem, they are just a specific version of the CSCS card. All you need to do for an ECS is pass a multiple choice Health and Safety test. The ECS card does however list a grading as per the JIB criteria, and this is where you might come a little unstuck, you'd unlikely be able to get graded as an electrician, but you could probably quite easily manage to get one with electricial trainee, or electrical labourer on it.
If they are just asking for an ECS, this is usually just from the POV of getting on sites (you generally cannot get on any resonable sized site without CSCS/ECS. If they want you to have any particular JIB grde this is normally requested separately, a lot of places will ask for JIBN approved (The three 'main' grades are Electrician, Approved Electrician, and then Technician).
My advice would be to get an ECS card as an electricial labourer or improver then sign upto an agency and see what they can get you onto, as long as you are vagely competant, arrive on site on time, dont take the **** with smoke breaks, then you'll be alright, no one expects anything too amazing from agency, you are only really expected to turn up with a tool bag and perhaps a drill driver, no vast expense of expensive tools or test gear needed. You might get stuck with liddling up miles of dado trunking or flexing up a never ending stream of light fittings to drop into grids at first, but you can progress from there.
